Piston-type accumulator

ABSTRACT

The invention relates to a piston-type accumulator comprising a separating piston ( 13 ) which can be displaced axially within a piston housing ( 1 ). Said piston separates a fluid side ( 15 ) of the accumulator from the gas side ( 23 ) thereof and comprises two sealing areas ( 17, 25 ) which are offset in relation to each other in the axial direction thereof, said sealing areas being arranged on the circumference thereof and being displaced on the inner wall of the accumulator housing. The invention is characterized in that the accumulator housing ( 1 ) is provided with a ventilation device ( 31 ) between said sealing areas ( 17, 25 ) for discharging leaking means passing through the sealing areas ( 17, 25 ).

[0001] The invention relates to a piston-type accumulator comprising a separating piston axially displaceable inside a piston housing, this piston separating a fluid side of the accumulator from its gas side and having two sealing areas axially offset from each other on its circumference in the inner wall of the piston housing.

[0002] Piston-type accumulators of this type are known in a large number of designs. The part of the piston housing surrounding the separating piston and extending axially generally is in the form of a cylindrical tube, for which reason the piston-type accumulator is often also termed a cylindrical accumulator. The sealing areas on the circumference of the separating piston customarily are made up of annular or O-ring seals which are seated in external circumferential grooves axially offset from each other in the separating piston.

[0003] Very high requirements are set, such as that of operation over wide temperature ranges, for example, between −40° C. and 150° C., from the viewpoint of the operating capacity of such cylindrical or piston-type accumulators. Test stand experiments have now shown that accumulators do not function satisfactorily with respect to long-term behavior, since gas often overflows toward the oil or fluid side. Such behavior is not acceptable in the case of accumulators which are to perform a safety function, especially if the accumulators involved are ones used in conjunction with hydraulic braking systems, in which overflow of gas into the hydraulic system could result in malfunctioning or even failure.

[0004] On the basis of this state of the art the object of the invention is to provide a piston-type accumulator which retains its sealing capacity even under extreme conditions and over long periods of operation and makes certain that gas cannot reach the fluid side under any operating conditions.

[0005] It is claimed for the invention that this object is attained with a piston-type accumulator of the type indicated in the foregoing in that the piston housing has, at a point situated between the sealing areas of the separating piston, an overflow feature for discharge of leakage media overflowing the sealing areas.

[0006] The overflow feature positioned between the sealing areas on the gas side and the fluid side makes certain that media cannot overflow from the gas side to the fluid side or in the opposite direction, even if molecules of the media adjacent to the separating piston make their way through the otherwise tight sealing system on the circumference of the separating piston. Because of the small molecules on the medium situated on the gas side, nitrogen in most cases, some penetration of the sealing rings provided on the separating piston cannot be completely eliminated even if the surface on the inside of the cylindrical tube of the piston housing has been subjected to the most precise machining, because of the requirement by definition that there is very little friction between the piston seal and the inside of the cylindrical tube during piston movement, a requirement which does not allow high surface pressure. Even in the event of passage of leaks, of hydraulic fluid, for example, through the piston seal from the fluid side, because of the overflow feature they cannot penetrate the gas side.

[0007] The piston-type accumulator claimed for the invention is suitable in particular for applications in which safety requirements must be met, for braking systems in particular, since prevention of passage of gas molecules to the fluid side is of decisive importance in this situation.

[0008] A vent opening drilled through the wall of the piston housing may be provided as an overflow feature.

[0009] In one advantageous embodiment the discharge end of the vent opening communicates with a collecting chamber receiving the leakage media. As a result, leakage media are discharged to the exterior only after the collecting chamber has been filled. The configuration may be such in this instance that the discharge of the collecting chamber has a normally closed valve layout which is opened by the pressure prevailing in the collecting chamber, so that automatic discharge occurs when a predetermined pressure builds up after the collecting chamber has been completely filled.

[0010] In the case of an embodiment as a “supertight” piston-type accumulator, an additional third sealing area positioned even closer to the gas side may be provided in addition to the sealing areas between which the overflow feature is positioned. Since passage of leakage components from the fluid side is possible, the piston seal forming the third sealing area and normally the piston seal forming the second sealing area as well would run dry. In one advantageous exemplary embodiment of the invention a supply device is provided in the separating piston for delivery of a free-flowing lubricant to the circumferential section of the separating piston positioned between the second and third sealing areas of the separating piston. Such lubricant may be a high-viscosity oil such as a mineral oil or a free-flowing lipid. In addition to the lubrication achieved by this configuration, as a result of which piston friction is reduced and the service life extended, an additional blocking or sealing effect is obtained because of the high viscosity of the substance delivered.

[0011] The invention is explained in detail in what follows on the basis of an exemplary embodiment presented in the drawing. The sole figure shows a longitudinal section in simplified diagrammatic form of the exemplary embodiment of the piston-type accumulator.

[0012] The piston-type accumulator shown in the drawing has a piston housing designated as a whole as 1 with a cylindrical tube 3 which is closed on one end by an end wall 5 shaped so as to be integral with the cylindrical tube 3 and on the opposite end by a sealing cover 7. In the example illustrated the sealing cover 7 is fastened to the cylindrical tube 3 by a snap ring 9 and sealed on the inner wall of the cylindrical tube 3 by mean of an O-ring 11. Use of a snap ring 9 could be replaced by welding of the sealing cover to the cylindrical tube 3.

[0013] Mounted in the cylindrical tube 3 so as to be axially displaceable is a separating piston 13 which is sealed off from the superfinished inner wall of the cylindrical tube 3 by means of three piston seals axially offset from each other which form a first, second, and third sealing area on the circumference of the separating piston 13. The piston seals are each represented by sealing rings seated in circumferential grooves in the separating piston 13, the sealing ring 17 nearest the fluid side 15 of the piston-type accumulator forming the first sealing area. A passage 19 with a connecting sleeve 21 effects connection to an associated hydraulic system (not shown).

[0014] A second sealing ring 25 seated in a circumferential groove in the separating piston 13 is provided as the second sealing area, axially offset from the sealing ring 17 forming the first sealing area, toward the gas side 23 adjacent to the other side of the piston. A third sealing area offset even further in the direction of the gas side 23 is formed by a third sealing ring 27 seated in a circumferential groove 13 in the separating piston.

[0015] The path of the stroke of the separating piston 13 inside the cylindrical tube 3 is limited to a desired operating stroke length by mechanical means, stops (not shown) in the cylindrical tube, or, as an alternative, by controlling the pressure relationships of fluid side 15 and gas side 23, the gas charging pressure of which may be adjusted by way of a charging connection 29. In the area of the cylindrical tube 3, which extends over the entire operating stroke length of the separating piston 13 between the first and the second sealing area, that is, between sealing ring 17 and sealing ring 25, a vent opening 31 extending through the wall of the cylindrical tube 3 is formed as an overflow feature which permits discharge of leakage media. A recess in the shape of an annular groove 33 with beveled side edges extending over the entire circumference of the inner wall is made in the inner wall of the cylindrical tube 3 in the area of the interior outlet of the vent opening 31. The recess 33 also prevents shearing off of the seals 25 and 27 during assembly when these seals are pushed over the opening 31. Together with a recess 37 made in the circumference of the separating piston an inner chamber communicating with the vent opening 31 is formed into which leakage media may enter should migration of fluid molecules through the sealing ring 17 occur or should the sealing rings 27 and 25 be penetrated by the small gas molecules of the charging gas on the gas side 23. Any such leakage media pass through the vent opening 31 into a collecting chamber 39 with which the outer end of the vent opening 31 communicates.

[0016] In the exemplary embodiment illustrated this collecting chamber 39 is formed by an annular element 41 seated on the outside of the cylindrical tube 3. This annular element is a shaped element of plastic or sheet metal integrated with a flat outer annular surface 43 which is set laterally in edge strips 45 extending vertically relative to it, the free ends of which edge strips 45 rest on the exterior of the cylindrical tube 3 so that the annular surface 43 is kept equidistant from the exterior of the cylindrical tube 3. The edge strips 45 are sealed off from the exterior of the cylindrical tube 3 by O-rings 47. The collecting chamber 39 as thus formed has as outlet to the exterior an opening 49 which is opened or closed by a valve system. An elastic band 51 here surrounds the annular surface 43 of the annular element 41. The initial tension selected which the band 51 applies to the annular surface 43 is such that the band 51 is lifted from the opening 49 when a predetermined excess pressure is present in the collecting chamber 39 so as to discharge the leakage media present in the collecting chamber 39 into the environment.

[0017] In the figure the opening 49 forming the outlet is shown on the top side of the cylindrical tube 3 in the drawing. In order to make it possible for the overflow feature to extend upward no matter how the piston-type accumulator is mounted, the annular element 41 is rotatable on the cylindrical tube 3 in order to make it possible for the opening 49 to be adjustable to the highest position.

[0018] In place of sealing the collecting chamber 39 off from the cylindrical tube 3 by means of the O-rings 47 the ends of the edge strips 45 could be configured as sealing edges acting directly in conjunction with the cylindrical tube 3. In place of a clear through vent opening 31 an opening containing a porous plug-like insert might be provided, for example, by use of a plug of a porous sintered material.

[0019] An annular groove 53 which communicates with a supply device for supply of a free-flowing lubricant is made in the circumferential area of the separating piston 13 which is positioned between the second and third sealing area, that is, between sealing rings 25 and 27. The separating piston 13 has for this purpose a concentric auxiliary cylinder 55 which is mounted in the interior and which is closed in the direction of the fluid side 15 and open in the direction of the gas side 23. An auxiliary piston 57 is introduced from the direction of the gas side into the auxiliary cylinder 55. This auxiliary piston 57 has a circumferential piston seal 59 and is secured against escape from the auxiliary cylinder 55 by a snap ring 61. The enclosed space situated between the auxiliary piston 57 and the closed end of the auxiliary cylinder 55 is filled with a supply of a free-flowing lubricant. A connecting channel 63 connects this lubricant supply space to the annular groove 53 on the circumference of the separating piston 13.

[0020] The auxiliary piston 57 is spring loaded by a helical pressure spring 65 which rests on a retaining plate 69 secured on the separating piston 13 by means of a snap ring 67. Consequently, the auxiliary piston 57 is subject not only to the pressure of the gas side 23, but to the initial tension of the spring as well, so that the auxiliary piston 57 in the compartment containing the supply of lubricant generates a delivery pressure by which the lubricant is pressed into the annular groove 53. The lubricant is a high-viscosity oil or a free-flowing lipid. As a result, a blocking or sealing effect is produced in the relevant areas of the separating piston 13 in addition to lubrication of the sealing rings 25, 27. On the whole especially good long-term behavior of the piston-type accumulator is obtained, in particular complete safety from escape of the medium on the gas side 23 to the fluid side 15, so that the piston-type accumulator claimed for the invention is especially well suited also for use in braking systems.

[0021] The elastic band 51 covering the opening 49 may also be replaced by another ring-shaped elastic element such as one in the form of an O-ring or a ring rectangular in cross-section, or the like.

[0022] As is shown by the illustration in particular, the possibility also exists of introducing into the interior of the housing a stop element 70 in the form of a bushing; this stop element 70 prevents the seal 17 from sliding into the groove 33 should the separating piston 13 return to a much higher position (not shown). The external circumference of the respective stop element 70 rests flush against the interior circumference of the piston housing 1 and otherwise extends between the end wall 5 and one free end of the separating piston 13 when, as shown in the figure, this piston comes to rest against the stop element 70. The stop element 70 is otherwise fixed by its inherent tension inside the piston housing 1 in its position as illustrated. The stop element may also be replaced by a projection or other stop means on the inside of the piston housing 1, the configuration selected obviously being such that the sealing means 17 cannot reach the groove 33 when the device is in operation. 

1. A piston-type accumulator having an axially displaceable separating piston (13) inside a piston housing (1), such separating piston (13) separating a fluid side (15) of the accumulator from its gas side (23) and having on its circumference extending over the inner wall of the piston-type accumulator (1) two sealing areas (17, 25) offset from each other in the axial direction, characterized in that the piston housing (1) has, at a point situated between the sealing areas (17, 25) of the separating piston (13), an overflow feature (31) for discharge of leakage media penetrating the sealing areas (17, 25).
 2. The piston-type accumulator as claimed in claim 1, wherein a vent opening (31) configured to extend through the wall of the piston housing (1) is provided as an overflow feature.
 3. The piston-type accumulator as claimed in claim 2, wherein the outlet end of the vent opening (31) communicates with a collecting chamber (39) for reception of leakage media.
 4. The piston-type accumulator as claimed in claim 3, wherein the collecting chamber (39) has an outlet (42) allowing venting to the exterior.
 5. The piston-type accumulator as claimed in claim 3, wherein the outlet (49) has a normally closed valve system (51) which may be opened by the pressure prevailing in the collecting chamber (39).
 6. The piston-type accumulator as claimed in claim 3, wherein the collecting chamber (39) is in the form of an annular element (41) seated on the outside of the separating piston (13) and receiving the cylindrical tube (3) of the piston housing (1), the annular surface (43) of which annular element (41) extending equidistant from the outside of the cylindrical tube (3) is retained at a distance defining the clear width of the collecting chamber (39) by edge strips (45) adjoining the annular surface (43) and projecting radially inward.
 7. The piston-type accumulator as claimed in claim 6, wherein the annular surface (43) has an opening (49) forming the outlet and positioned between the two side edge strips (45).
 8. The piston-type accumulator as claimed in claim 7, wherein an elastic band (51) surrounding the annular surface (43) and covering the opening (49) is provided as valve system of the outlet.
 9. The piston-type accumulator as claimed in claim 6, wherein the insides of the edge strips (45) facing each other are each sealed off by a sealing element (47) from the outside of the cylindrical tube (3).
 10. The piston-type accumulator as claimed in claim 1, wherein the separating piston (13) has a recess (37) made in its circumference in the section of the piston (13) positioned between the sealing areas (17, 25) and used in conjunction with the overflow feature (31).
 11. The piston-type accumulator as claimed in claim 1, wherein the separating piston (13) has, in addition to the first sealing area (17) adjacent to the fluid side (15) and the second sealing area (25) offset axially toward the gas side (23), a third sealing area (27) offset even further toward the gas side (23) and wherein in the separating piston (13) a supply device (55, 57, 63) is provided for delivery of a free-flowing lubricant to the circumferential section (53) of the separating piston (13) situated between the second and third sealing areas (25 and 27).
 12. The piston-type accumulator as claimed in claim 2 wherein the interior end of the vent opening (31) communicates with a recess in the shape of an annular groove (33) made in the inner wall of the piston housing (1), which recess in the shape of an annular groove (33) extends through on the inner circumference side in a direction perpendicular to the axial direction. 